‘The possibility of the end of sex… is very real’
Reproduction used to be a simple thing: two parents, one egg, one sperm, one embryo, one baby. But on Friday, a study published in Cell complicated — or simplified, depending on who you ask — the arithmetic. Researchers report that they have successfully created mouse fetuses without using sperm and eggs — a scientific first.
In place of the usual starting materials, the team, led by researchers at the Salk Institute for Biological Studies in California and the University of Texas Southwestern Medical Center, used specialized stem cells that can theoretically turn into any adult cell or cell needed to make an embryo. In a dish, these cells grew and self-assembled into embryo-like structures that were transferred into mouse wombs and started to grow like fetuses.
Some of those extended pluripotent stem cells, or EPS cells, were derived from ear cells, suggesting that sexual reproduction may no longer be necessary. But senior author Jun Wu, PhD, says that’s not what this research is about.
“The goal of this research at this stage is certainly not ‘end of sex’ for reproduction,” Wu, an assistant professor at UT Southwestern Medical Center, tells OneZero in an email. “The primary goal is to understand early development.”
Scientists have been trying to create embryos from scratch for years. In 2016, Chinese researchers successfully created mouse sperm from stem cells, which they then used to fertilize regular eggs and produce healthy babies. Last year, another team from China manipulated mouse sperm and egg DNA to produce healthy offspring from same-sex mouse couples, and researchers in Japan coaxed human blood cells to become egg cell precursors.
What makes the new work different is that it didn’t rely on sperm or eggs at all. The EPS cells that the team started with have the special ability to turn into all three cell types needed to form an early embryo, called a blastocyst. Those cells are crucial if you want the early embryo to develop.
Supported by a rich broth of growth factors and other nutrients, the EPS cells grew and self-assembled into embryos. When they were transplanted into mouse wombs, some of them implanted and began to develop like any embryo produced the old-fashioned way might.
The goal of this research at this stage is certainly not ‘end of sex’ for reproduction.
But they weren’t perfect. They didn’t implant into the uterus as efficiently as natural embryos, and their tissues seemed “not properly organized,” says Wu. He suspects that the process they developed doesn’t “recapitulate all the aspects” of natural embryo formation and that the growth conditions weren’t quite right; it’s possible, too, that they’re missing some important factors that only egg cells carry. But the team is working on it, not only in mice but in humans. “And we are testing whether human EPS cells can also [generate] similar structures,” Wu says.
Even if they succeed, it’s not likely that scientists will try to make human babies from scratch, at least not anytime soon. Eli Adashi, M.D., former dean of biomedical sciences at Brown University and reproductive health expert, tells OneZero, “I don’t think anybody at this point thinks of this as a clinical tool or is anything related to infertility.” However, he says it gives us a glimpse into how embryos form — and sometimes fail to — opening up new avenues to prevent miscarriage and terminated pregnancies.
Besides, he points out, if it’s the end of sex we’re worried about, you could argue it’s already here. “The possibility of the end of sex for procreation versus recreation, I think, is very real,” he says. It began with IVF, which allows gestation without sex, and rather than seeing stem cells turned into human embryos, he thinks it’s far more likely we’ll see them turned into human eggs and sperm, which could overcome a number of reproductive issues: males born without sperm, premature menopause, inherited infertility, and the challenges of collecting eggs for IVF.
“That’s something that’s going to happen in a reasonable period of time,” he says.
However, he notes, “I don’t think we can foresee all the possibilities.”
Wu appears to keep an open mind. “Ultimately, although [it] remains science fiction at this stage, it’ll be fantastic if we can achieve the goal of generating viable embryos without sperm or eggs in the future,” he says. “But there is still a long way to go since there is still a lot of unknowns during early development.”